1. Field of the Invention
The present invention relates to a method of controlling the density and/or distribution of a vapor deposition flow of a material vaporized from a vaporization object by a beam of electrons in a treatment chamber.
It also relates to an arrangement for a controlling of the density of the vapor deposition flow and/or its distribution in a treatment chamber of a material vaporized from a vaporization object by means of a beam of electrons.
2. Description of the Prior Art
Throughout the description we use the following definitions:
vapor flow: the amount of evaporated material passing per time unit across a surface area PA1 vapor flow density: vapor flow passing across a unit of area PA1 vapor flow density distribution: the characteristic of vapor flow densities considered in two dimensions over a surface area PA1 standardized distribution: the distribution characteristic normalized by the maximum density occurring along the surface area considered PA1 power density: power per unit area PA1 power density distribution: power density characteristic considered in two dimensions over a surface area PA1 temperature distribution: temperature characteristic considered in two dimensions over a surface area PA1 evaporation rate: amount of material evaporated per time unit PA1 deposition vapor flow: vapor flow which is deposited on a desired surface area
The standard power density distribution p/p.sub.max of a beam of electrons used for the evaporating of a material, usually termed target, is substantially bell-shaped such as illustrated in FIG. 1.
At a model beam S.sub.m of an assumed homogeneous, standardized power density distribution p/p.sub.max the standardized temperature distribution .theta./.theta..sub.max is also substantially bell-shaped in the vaporization area acted upon by the beam, specifically due to the diffusion of the heat, such as illustrated FIG. 2a. Accordingly, in when regarding the power density as not being homogeneously distributed, as for a real beam according to FIG. 1 where distribution is quite pronounced, peripherically decreasing standardized temperature distribution is produced such as illustrated in FIG. 2b with a pronounced temperature peak at the center area of the vaporization surface.
Apart from a high thermal loading of the material being vaporized, i.e. of the target material, this leads among others at a high beam power to deformations of the vaporization surface (target surface) such as shown in "Elektronenstrahltechnologie", S. Schiller et al., Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, 1977, page 174. (Schiller) If the beam power is changed at a fixed, standardized distribution of the power density, the rate of evaporation, defined as the amount of material vaporized per unit of time from the vaporization object, runs through a pronounced maximum such as illustrated in Schiller on page 173.
The vapor flow which spreads from the area of impingement of the beam of electrons leads in the treatment space, considered locally, to varying densities of the vapor flow.
From the standardized power density distribution of the beam, the power of the beam, and depending on standardized density distributions of vapor flow result, in the treatment space such as disclosed, for example in the mentioned book, at page 142.
The occurrence of spatters at too high a beam power and at a given standardized density distribution is one of the limits to the evaporation-rate. Further increase in the evaporation-rate would be desirable, however, to increase the economics of such process. A second corresponding limit is to the co-changing of the density distribution of the vapor flow. See, for example, Schiller, page 142.
There is an inherent need to increase the density of the vapor flow in order to increase productivity, whereas the selection of an optimal distribution of vapor flow density depends on the type of deposition process, such as for instance how workpieces to be coated by electron beam vaporization are positioned in the treatment space or which coating profile is desired.
Without the above mentioned limits it thus would be possible to increase productivity by an increase in the evaporation rate or, an increase of vapor flow at the coating location or locally, an increase in the density of vapor flow. This would result from an increase of the power of the electron beam acting on the evaporation surface area.
The quality of the coating and the productivity of a plant, as well, could be further increased by aimed optimizing of the distribution of vapor flow density (exploitation of space!). Because the maximum of the evaporation rate does not generally occur at the same beam power (at a standardized distribution of power density which is kept constant) as a process specific, desired distribution of vapor flow, it would be desirable to optimize either the density of deposition vapor flew or the deposition vapor flow density, or to design the deposition vapor flow density and the deposition vapor flow density distribution specific to a given plant, optimally considering economic aspects.